Mold assembly apparatus and method for molding metal articles

ABSTRACT

Apparatus assemblies and methods for melting and injection molding an article from a meltable metal that is sensitive to heating by radio frequency (RF) induction. An exemplary apparatus includes a mold including a cavity having a shape of an article to be molded, a delivery chute including a channel for delivering a solid metal billet from a proximal end of the delivery chute to a distal end which is adjacent to the mold, and an RF induction heating coil that surrounds the cavity of the mold and the distal end of the delivery chute. Advantageously, the portion of the mold defining the cavity and at least the distal end of the delivery chute (i.e., those portions surrounded by the RF coil) are formed of materials that are substantially insensitive to heating by RF induction so that the metal billet is melted and molded at approximately the same time.

RELATED APPLICATIONS

The present application claims the benefit of U.S. Patent ApplicationSer. No. 61/076,252, filed Jun. 27, 2008, entitled “MOLD ASSEMBLYAPPARATUS AND METHOD FOR MOLDING METAL ARTICLES”, and U.S. PatentApplication Ser. No. 61/076,258, filed Jun. 27, 2008, entitled “METHODSFOR MOLDING ORTHODONTIC BRACKETS FROM METAL”, the disclosure of each ofwhich is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to apparatus assemblies and methods formelting and molding metal articles from a meltable metal material.

2. The Related Technology

Metal articles can be manufactured in a variety of ways, includingmachining solid metal or injection molding the metal in the form of ametal powder mixed with a binder followed by sintering the green body toform the finished article. It is also possible to injection mold withmolten metal. Machining is often used to manufacture relatively smallnumbers of parts as the cost of the molds needed for injection moldingmetals are very expensive. If the number of articles to be manufacturedis large, injection molding may be preferred, as the molds can often beused repeatedly for tens of thousands or hundreds of thousands ofcycles.

When injection molding any article (e.g., from plastic or metal), themolten raw material is injected through a channel to the area definingthe article to be molded. When injection molding with molten metals, themetal is typically heated just prior to being forced towards the moldingcavity under tremendous pressure and heat. It is important to move themetal quickly so that it does not solidify by cooling before the moltenmetal can be introduced into the mold cavity. Typically the mold remainsrelatively cool so as to aid in cooling of the molded metal article andto prevent undue repeated temperature cycling of the mold, which resultsin premature wear and cracking of the mold. Because of this, the stateof the art typically relies on forcing the heated metal into the mold asquickly as possible.

When the article is removed from the mold, a portion of material, knownas a “runner” or “sprue” remains adhered to the article. The runner andsprue are a result of the excess material present within the channelsadjacent to the area of the mold cavity defining the article, whichsolidifies at the same time as the molded article. Technically, thesprue refers to that portion of material which solidifies within themain channel running from the reservoir of molten material to the moldcavity, while the runner refer to that portion of material whichsolidifies within the secondary channels connecting multiple moldcavities (i.e., runners convey molten material to the point(s) ofinjection at individual mold cavities). Often, a runner will connectmultiple molding chamber areas, such that multiple articles are moldedsimultaneously, all connected by one or more runners. The runners andsprues must be removed in a subsequent finishing/deburring step. For thesake of simplicity, runners and sprues will be referred to hereafter asrunners.

Recently, a new type of moldable metal, called “LIQUID METAL,” wasdeveloped and described in U.S. Pat. No. 6,682,611. Although this typeof metal has been touted as providing increased moldability, currentmolding apparatus and techniques, including those employed by themanufacturer of “LIQUID METAL” continue to yield molded products withattached runners and sprue.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods for meltingand injection molding an article from meltable metal. An exemplaryapparatus includes a mold including a cavity in the shape of an articleto be molded, a delivery chute including a channel for delivering aninitially solid metal billet having a mass equal to the molded articlefrom a proximal end of the delivery chute to a distal end which isadjacent to the mold and mold cavity, and a radio frequency (RF)induction heating coil that surrounds the cavity of the mold and thedistal end of the delivery chute. Advantageously, the mold defining themold cavity and at least the distal end of the delivery chute (i.e., theportion surrounded by the RF coil) are formed of materials that aresubstantially not sensitive to heating by RF induction. Such aconfiguration allows for activation of the RF induction coil withoutsubstantial heating of the mold and the adjacent portion of the deliverychute. The apparatus is used to mold articles from metals which aresensitive to heating through RF induction.

In a related method of manufacture, an initially solid metal billet isintroduced into the channel of the delivery chute that leads to themolding cavity of the mold. The metal billet is selectively heated andmelted by activating the RF induction heating coil when the metal billethas dropped down the channel to a location surrounded by the RFinduction heating coil, just before the material enters the adjacentmold cavity. The apparatus may include one or more gates along thelength of the delivery chute so as to hold the metal billet at the gatelocation until the gate is opened to allow passage further into thechannel, towards the molding cavity. Advantageously, the activation ofthe RF induction coil results in substantially no direct heating of thedelivery chute or the mold because of the materials (e.g., ceramic) fromwhich these structures are formed. As a result of heating by the RFinduction coil, the metal billet melts, allowing the molten metal toflow into the molding cavity of the mold. The RF induction coil mayremain activated as long as necessary to ensure that the metal fills themolding cavity. Because the metal billet can have a mass and volumesubstantially equal to the mass and volume of the finished moldedarticle, all of the molten metal enters the cavity with little or noexcess. Once the metal fills the molding cavity, the RF induction coilis deactivated so as to allow the molten metal in the molding cavity tosolidify by cooling so as to form the molded metal article.

The molded article is allowed to solidify, which may occur relativelyquickly because the mold is cool relative to the molten metal within themolding cavity. The mold acts as a heat sink to draw the heat quicklyout of the molten metal through cooling and solidification of the moldedarticle. The mold may further include cooling lines (e.g., runningthrough the mold) to draw heat away from the mold to prevent build up ofheat within the mold through repeated molding cycles.

The inventive apparatus and methods make it possible to mold metal partsthat have minimal or no excess metal attached to the molded part (i.e.,in the form of a runner and/or sprue). This, in turn, minimizes oreliminates the need for post molding machining or debriding to removethe excess metal. Of course, the molded parts can be machined orpolished as desired to yield a final part suitable for an intended use.

These and other advantages and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 is a perspective view of an exemplary apparatus for molding metalarticles according to one embodiment of the present invention;

FIG. 2 is a right side view of the apparatus of FIG. 1;

FIG. 3 is front side view of the apparatus of FIG. 1;

FIG. 4 is a cross-sectional view of the apparatus of FIG. 1;

FIG. 5 is a perspective view of the apparatus of FIG. 1, with the moldin a raised position so that the RF induction heating coil surrounds themold cavity;

FIG. 6A is a close up perspective view of one side of the mold cavityand surrounding mold of FIG. 5;

FIG. 6B is a close up perspective view of the opposite side of the moldcavity and surrounding mold of FIG. 5;

FIG. 7A is a cross-sectional view of the apparatus of FIG. 5, in which ametal billet rests against the closed first gate member;

FIG. 7B is a cross-sectional view of the apparatus of FIG. 5, in whichthe metal billet of FIG. 7A passes through the open first gate member;

FIG. 8A is a cross-sectional view of the apparatus of FIG. 5, in whichthe metal billet of FIG. 7A rests against the closed second gate member;

FIG. 8B is a cross-sectional view of the apparatus of FIG. 5, in whichthe metal billet of FIG. 7A passes through the open second gate member;

FIG. 9 is a cross-sectional view of the apparatus of FIG. 5, in whichthe metal billet of FIG. 7A is being melted by activation of the RFinduction heating coil;

FIG. 10 is a cross-sectional view of the apparatus of FIG. 5, in whichthe pressing member forces all molten metal into the cavity;

FIG. 10A is a close up view of a contact surface of the pressing memberof FIG. 10;

FIG. 10B is a close up view of the filled mold cavity after the pressingmember forces all molten metal into the cavity and applies a patterninto the exposed surface of the metal within the cavity;

FIG. 11 is a cross-sectional view of the apparatus of FIG. 5, in whichthe pressing member and mold have been retracted;

FIG. 12 is a cross-sectional view of the apparatus of FIG. 5, in whichthe mold has been rotated 180° and the molded metal article removed fromthe mold cavity;

FIG. 13 is a perspective view of the molded metal bracket;

FIG. 14 is a side view of the bracket of FIG. 13 once the bonding pad ofthe bracket has been bent so as to create undercuts within the pressedin pattern;

FIG. 15A is a perspective view of an alternative bracket that may bemolded according to the inventive method; and

FIG. 15B is a perspective view of another alternative bracket that maybe molded according to the inventive method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction

The present invention is directed to apparatus and methods for meltingand injection molding an article from a meltable metal. An exemplaryapparatus includes a mold including a cavity having a shape of anarticle to be molded, a delivery chute including a channel fordelivering an initially solid metal billet from a proximal end of thedelivery chute to a distal end which is adjacent to the mold, and aradio frequency (RF) induction heating coil that surrounds at least thecavity of the mold and the distal end of the delivery chute.Advantageously, at least a portion of the mold and at least the distalend of the delivery chute (i.e., those portions surrounded by the RFcoil) are formed of materials that are substantially insensitive toheating by RF induction.

According to one aspect, the present invention is directed to apparatusand methods for melting and injection molding an orthodontic bracketfrom a meltable metal. According to one method, an initially solid metalbillet from which a single orthodontic bracket is to be formed isselectively heated by RF induction heating adjacent to a mold cavity ofa mold. According to one embodiment, at least that portion of the molddefining the mold cavity may be formed of a material that is notinsensitive to heating by RF induction, and the mold cavity is in theshape of an orthodontic bracket or portion thereof to be formed. Theadjacent delivery channel or chute may also comprise a material that isinsensitive to heating by RF induction.

The metal billet is selectively heated and melted by activating an RFinduction heating coil when the metal billet is in the delivery channelor chute adjacent (e.g., just above) the mold cavity and surrounded bythe RF induction heating coil. As a result of heating by the RFinduction coil, the metal billet melts, allowing the molten metal toflow into the mold cavity of the mold. The RF induction coil may remainactivated as long as necessary to ensure that the metal fills the moldcavity. Because the metal billet can have a mass and volumesubstantially equal to the mass and volume of the finished moldedbracket (and the volume of the billet can be substantially equal to thevolume of the mold cavity), all of the molten metal can enter the cavitywith little or no excess. Once the metal fills the mold cavity, the RFinduction coil may be deactivated so as to allow the molten metal in themolding cavity to solidify by cooling so as to form the molded metalbracket.

II. Exemplary Molding Apparatus

FIGS. 1-4 illustrate an exemplary molding apparatus 100 including a moldassembly 102, a delivery chute 104, and an RF induction heating coil106. Mold assembly 102 includes a first portion 108 a and a secondportion 108 b, with a mold cavity 110 defined between the two portions108 a and 108 b, respectively. In the illustrated configuration, moldportion 108 b is mounted on a carriage 112 so as to allow slidingmovement of portion 108 b away from portion 108 a so as to open themold. Advantageously, the portion of mold assembly 102 including moldcavity 110 is configured as a cylinder 114 to allow the cylinder to bereceived within RF induction coil 106. Of course, other configurationsof portion 114 may be possible (e.g., a square cross-section or othercross-section small enough to be received within coil 106).

As perhaps best seen in the cross-sectional view of FIG. 4, deliverychute 104 includes an internal channel 115 that runs from a proximal end116 to a distal end 118, which is adjacent to the mold cavity 110 whenmold assembly 102 is in a raised position. In the illustratedconfiguration, chute 104 is oriented at an angle relative to a verticalaxis Y, and the apparatus further includes a pressing member 120 alongvertical axis Y for selectively pressing a molten metal billet intomolding cavity 110. The illustrated embodiment of delivery chute 104further includes first and second gate members 122 and 124,respectively, for selectively impeding and allowing movement of a metalbillet through channel 115 towards molding cavity 110. Such a doublegate configuration may be particularly helpful if the heating, melting,and subsequent cooling of the meltable metal billet is to be carried outunder vacuum or in an inert atmosphere. Pressing member 120 is disposedwithin a vertical press housing 121 aligned with axis Y. Pressing member120 slides within a channel defined by an upper portion 117 and a lowerportion 115, which also serves as the distal portion of delivery channel115.

At least portion 114 of mold 102 (i.e., that portion which is receivedwithin surrounding RF induction heating coil 106) is formed of amaterial that is substantially insensitive to heating by RF induction.At least the distal portion 118 of delivery chute 104 (i.e., thatportion which is received within surrounding RF induction heating coil106) is also formed of such a material so that the apparatus allowsselective heating and melting of just the metal billet introduced intochannel 115, without any substantial direct heating of mold portion 114or distal end 118 of delivery chute 104 by RF induction heating coil106. Advantageously, the heating induced by coil 106 is limited to justthe metal billet to be used in molding the metal article. In addition,the heating and melting is performed immediately prior to molding, suchthat melting and molding are performed at approximately the same time.Because the billet can have the same or similar volume as mold cavity110, there is no need to maintain a stream of metal in a molten state asit travels from a reservoir to the mold cavity.

An example of a material that is substantially insensitive to heating byRF induction include various ceramics. Suitable ceramics preferably willbe substantially smooth and non-porous so as to aid in removal of themolded article. One specific example of an exemplary ceramic that may beused includes a partially stabilized zirconia ceramic. One suchmaterial, Mg-PSZ, is available from Carpenter Advanced Ceramics locatedin Reading, Pa.

The RF induction coil 106 is configured to induce melting of a metalbillet just prior to the metal entering the mold cavity. Coil 106 may beoperated so that the metal material may be heated until the metalmaterial completely fills the mold cavity 110, and longer, if needed.The design and operating parameters of the RF coil 106 may depend on thecomposition of the metal being melted, heat capacity of the metal beingmelted, electrical and thermal conductivity of the metal, the mass ofthe metal billet being melted, the number of windings present within thecoil 106, the current, voltage, and frequency applied through the coil,among other things. Suitable commercial RF induction heating coilsystems are available from Ameritherm, located in Scottsville, N.Y.Suitable designs and operating parameters will be apparent to oneskilled in the art in light of the present disclosure.

For example, it may be preferable to provide sufficient induced currentand heat to the metal billet so as to melt the billet within about 5seconds or less, more preferably within about 3 seconds or less, andmost preferably within about 1 second or less. Ideally, melting isachieved almost instantaneously (e.g., within about 0.1 second). Themetal is heated at least to its melting temperature so as to melt themetal. Preferably, heating may be performed to at least about 2° C.above the melting temperature of the metal, more preferably at leastabout 5° C. above the melting temperature of the metal, and mostpreferably at least about 10° C. above the melting temperature of themetal. In addition, it may be desirable to heat the metal no higher thanabout 50° C. above its melting temperature so as to reduce energyconsumption, as the heat must later be removed during solidification andcooling of the molded article.

Any metal material that can be heated and melted through subjecting thematerial to RF induction may be molded with the inventive apparatus andmethod. Exemplary materials include, but are not limited to silver,iron, steel, other iron containing metal alloys, gold, nickel-titaniumalloys, titanium alloys, and “LIQUID METAL”, which refers to specificzirconium based metallic amorphous glass-like alloys formed from lowpurity materials, preferred examples of which include the addition of asmall amount of yttrium (Y). Disclosed examples of such materials are acombination of Zr, Al, Ni, Cu and Y or Zr, Ti, Ni, Cu, Be, and Y.Examples of LIQUID METAL alloys are disclosed in U.S. Pat. No.6,682,611, incorporated herein by reference. Specific examples of LIQUIDMETAL amorphous alloys disclosed in U.S. Pat. No. 6,682,611 include(Zr₄₁Ti₁₄Cu_(12.5)Ni₁₀Be_(22.5))₉₈Y₂, (Zr₃₄Ti₁₅Cu_(12.5)Ni₁₁Be₂₈)₉₈Y₂,Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈Y₂, (Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈)₉₈Y₂,(Zr₃₄Ti₁₅Cu₁₀Ni₁₁Be_(22.5))₉₈Y₂, (Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₈Y₂, and(Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₆Y₄.

As noted above, although LIQUID METAL may provide increased moldabilityrelative to traditionally used metals, current molding apparatus andtechniques continue to yield molded products with attached runners andsprue, limiting the utility of the material to date. In the case ofLIQUID METAL, heating and melting of the metal, as well as cooling, isperformed under vacuum (or possibly in an inert atmosphere, for exampleof argon, helium, or nitrogen), as LIQUID METAL oxidizes when heated inair, which is undesirable. As a practical matter, the entire process maybe performed under such conditions.

The apparatus and related methods may be used to form various metalarticles, for example, orthodontic brackets (e.g., as illustrated inFIG. 13), small gears for craftsman quality analog watches, gold, silveror other metallic jewelry, springs, or any other small metal article.Advantageously, there is little or no excess metal (i.e., runners and/orsprue) that remain adhered to the molded article when released from themold. This reduces or eliminates the need for post molding finishing ormachining. In addition, it reduces or eliminates costs associated withrecycle of the material making up the runners and/or sprue. Reductionand/or elimination of finishing steps (e.g., polishing, grinding,deburring) is particularly beneficial when working with LIQUID METALalloys containing beryllium, as beryllium has been found to becarcinogenic.

III. Exemplary Method of Use

According to one embodiment, mold assembly 102 can be vertically raisedand lowered. For example, as shown in FIG. 1 the mold cavity withincylindrical portion 114 is shown retracted relative to RF induction coil106, and in FIG. 5 it is shown raised so that the mold cavity withinportion 114 is inserted within and surrounded by RF induction coil 106.FIGS. 6A and 6B illustrate the separate halves 110 a and 110 b of moldcavity 110 within cylindrical mold portion 114. In the illustratedexample, the mold cavity 110 is in the shape of a non self-ligatingorthodontic bracket to be molded of metal (e.g., a LIQUID METAL alloy).Brackets of other shapes, even single piece self-ligating brackets, mayalso be similarly formed. Two-part self-ligating brackets (e.g.,including a bracket base and a separate hinged or sliding cover) may bemolded in two or more parts (i.e., a mold cavity for the base andanother mold cavity for the cover, and then assembled together).

As best seen in FIGS. 6A-6B, there is no runner connected to mold cavity110, but rather the portion of mold cavity 110 that forms the bondingpad of the orthodontic bracket is adjacent the top surface 126 of moldportion 114. Advantageously, the metal billet passes through deliverychannel 115 in solid phase right up to molding cavity 110, where it ismelted by RF induction at approximately the same time it is introduced(e.g., by gravity and/or force of pressing member 120) into moldingcavity 110, reducing or eliminating the formation of any runner as aresult of metal cooling within a runner channel adjacent the moldcavity. In other words, melting may be accomplished only at the lastpossible moment, greatly simplifying the process related to maintainingthe material in a molten condition from melting until introduction intothe mold.

As seen in FIG. 7A, a metal billet 128 is introduced into channel 115 ofdelivery chute 104. In the illustrated example, chute 104 includes afirst gate member 122, which is initially closed so as to impedeprogress of billet 128 past gate member 122 until gate 122 is opened.Metal billet 128 may advantageously be of a mass that is approximatelyequal to the mass of the finished article. Assuming differences indensity at various temperatures and phases are negligible, billet 128 isalso of a volume that is approximately equal to the volume of the moldcavity 110. There is no runner channel that must be filled with themolten metal from the metal billet, as the solid metal billet 128 passesthrough the channel 115 to a location directly adjacent the moldingcavity 110. It is at this location that the billet 128 is melted atapproximately the same time as being introduced into the molding cavity110. There is no need for complex heating mechanisms to maintain the rawmetal in a molten state as it travels from a reservoir to the moldingcavity. This configuration advantageously reduces waste, subsequentfinishing steps required to finish the molded article, and recyclingcosts.

As shown in FIG. 7B, first gate member 122 is opened, allowing metalbillet 128 to pass through gate member 122 (e.g., by force of gravity)down towards second gate member 124 (see FIG. 8A). Second gate member124 may then be opened (see FIG. 8B), allowing billet 128 to continuedownward into the portion of channel 115 defined by press housing 121surrounded by RF induction heating coil 106. Gate members 122 and 124may be helpful in maintaining the heating, melting, and cooling steps ofthe method in a vacuum or inert atmosphere while allowing introductionof the metal billet 128 from atmospheric conditions. For example, gatemembers 122 and 124 are not opened simultaneously, but when gate member122 is opened, the vacuum or inert atmosphere within lower channel 115and mold cavity 110 is maintained by closed gate member 124. As shown inFIG. 9, upon activation of RF induction heating coil 106, metal billet128 quickly melts, and begins to flow down (e.g., by force of gravityand/or vacuum suction) into mold cavity 110.

In order to ensure that all of the molten metal is introduced into moldcavity 110, and to avoid the formation of any voids or bubbles withinthe cavity and finished molded metal article, pressing member 120 may beactivated, pressing all molten metal into the mold cavity (see FIG. 10).As shown in FIG. 10A, advantageously, the contacting surface 123 of thepressing member 120 may optionally include a pattern to be pressed intothe molten metal, particularly if the metal is already beginning to cooland solidify so that any such pressed shape would be retained within thesoft metal. For example, as perhaps best seen in FIG. 10B, a mesh orsawtooth pattern or other texture 125 may be pressed into the adjacentmolten metal so as to form a rough, textured, or uneven bonding pad forthe orthodontic bracket.

As perhaps best seen in FIG. 14, the bonding pad 127 of the orthodonticbracket 130 including the applied pattern 125 may be subsequently bentso as to achieve a desired curvature for aligning with the curved labialsurface of a tooth. Advantageously, such bending of the bonding pad 127alters the applied pattern so as to create undercuts within the bondingpad 127, which are advantageous in strongly bonding the bracket 130 to atooth. Such bending may be performed after the bracket 130 has beenreleased from the mold 110. Depending on the metal material of thebracket, heating of the bonding pad 127 may be required to achieve thedesired bending without fracture of the bracket. Of course, when moldingmetal articles of other shapes, different shapes or textures may bepressed into such a surface.

As shown in FIG. 11, after molten metal fills mold cavity 110 and isfurther pressed using pressing member 120, pressing member 120 isretracted to its original raised position, and the mold assembly 102 maythen be retracted from surrounding RF induction coil 106. This causesthe molded article within mold cavity 110 to quickly cool as a result ofthe relatively cool surrounding mold portion 114, which is insensitiveto heating from RF induction coil 106. In this way, the mold surroundingmold cavity 110 remains relatively cool (e.g., room temperature), whilethe molten metal fills mold cavity 110 and is forced therein by pressingmember 120. Heat, which may otherwise build up within mold assembly 102may be withdrawn through cooling lines (e.g., carrying a cooling fluidsuch as water or other liquid and/or gas) that may run through orotherwise exchange heat with the mold assembly 102.

As shown in FIG. 12, mold 102 may be rotated 180° (e.g., inverted) andopened as mold portion 108 b and the adjoining portion of cylindricalportion 114 slide along carriage 112, opening mold cavity 110 so thatmolded article 130 (e.g., an orthodontic bracket) may be removed. FIG.13 illustrates an exemplary orthodontic bracket 130 molded with theapparatus, although it will be understood that various other bracketconfigurations may be formed in a similar manner by altering the shapeof mold cavity 110. FIG. 14 shows a bracket having a curved bonding pad127 having a bonding pattern 125.

Exemplary alternative bracket configurations that may be formedaccording to the present method and apparatus are shown in FIGS. 15A and15B. FIG. 15A shows a two-part self-ligating bracket 230 including abracket base and a sliding ligation cover. The sliding cover and bracketbase may be molded as two separate parts and then assembled together.FIG. 15B illustrates a one-piece integral self-ligating bracket 330 thatmay be molded as a single piece from an amorphous metallic alloy (e.g.,LIQUID METAL). Glass-like LIQUID METAL alloys have been found tosurprisingly provide flexibility and resiliency when molded with verysmall cross sections, which allows the elongate film hinge connectingthe bracket base to the ligation cover of bracket 330 to resilientlyflex and bend as needed during opening and closing. The flexibility ofthe LIQUID METAL in the region of the film hinge connecting the bracketbase to the ligation cover allows the cover to be closed withoutfracture at the connecting film hinge.

In addition, articles of various other shapes (e.g., jewelry) may beformed in a similar manner by altering the shape of mold cavity 110. Asshown, the molded article requires little or no finishing, as there isno runner of unwanted metal material present to be removed after moldingof parts. Reduction and/or elimination of finishing steps (e.g.,polishing, grinding, deburring) which result in formation of metal dustis particularly beneficial when working with LIQUID METAL alloyscontaining beryllium, as inhalation of beryllium dust has been found tobe carcinogenic.

In addition, use of an RF induction heating coil and a ceramic orsimilar insensitive material for forming at least the portion of themold surrounding mold cavity 110 minimizes any temperature cycling ofthe mold assembly, reducing stress and wear on these parts.

Additional details regarding exemplary brackets and methods ofmanufacture by molding are disclosed in a United States PatentApplication bearing attorney docket number 7678.1087.2.1, filed the sameday as the present application, entitled ORTHODONTIC BRACKETS HAVING ABENDABLE OR FLEXIBLE MEMBER FORMED FROM AMORPHOUS METALLIC ALLOYS. Theabove patent application is hereby incorporated by reference.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. An apparatus for melting and molding an article from a solid metalbillet, comprising: a mold including a cavity having a shape of anarticle to be molded; a delivery chute including a channel fordelivering a solid metal billet from a proximal end to a distal end, thedistal end being adjacent to the cavity of the mold, at least thatportion of the mold defining the mold cavity and at least the distal endof the delivery chute being formed of a material that is substantiallynot sensitive to heating by RF induction; and an RF induction heatingcoil surrounding the cavity of the mold and the distal end of thedelivery chute.
 2. An apparatus as defined in claim 1, wherein at leastthe mold and distal end of the delivery chute are contained with achamber under vacuum or an inert atmosphere.
 3. An apparatus as definedin claim 1, wherein the delivery chute further comprises at least onegate member for selectively allowing passage of a metal billet throughthe channel.
 4. An apparatus as defined in claim 1, further comprising apressing member for selectively pressing a molten metal billet into thecavity.
 5. A apparatus as recited in claim 4, wherein the pressingmember includes a contacting surface having a mesh, sawtooth, ortextured pattern.
 6. An apparatus as defined in claim 1, wherein atleast the portion of the mold defining the mold cavity is formed ofceramic.
 7. An apparatus as defined in claim 1, wherein at least thedistal end of the delivery chute is formed of ceramic.
 8. A method ofmanufacturing a molded metal article, comprising: introducing a solidmetal billet into a delivery chute having a channel leading to a moldingcavity of a mold, at least that portion of the mold defining the cavitybeing formed of a material that is not sensitive to heating by RFinduction; selectively heating the metal billet by RF induction heatingadjacent the mold cavity so as to melt the metal billet such that themetal fills the molding cavity without substantial heating of the mold;allowing the metal within the molding cavity to cool so as to form ametal molded article; and removing the metal article from the moldingcavity.
 9. A method as recited in claim 8, wherein the volume of themetal billet is substantially equal to the volume of the mold cavity,the method further comprising maintaining the metal in a heated moltenconfiguration until substantially all metal material has entered themolding cavity and the cavity is substantially filled.
 10. A method asrecited in claim 8, wherein at least that portion of the mold definingthe mold cavity is formed of ceramic.
 11. A method as recited in claim8, wherein at least the distal end of the delivery chute is formed of amaterial that is insensitive to heating by RF induction.
 12. A method asrecited in claim 11, wherein at least the distal end of the deliverychute is formed of ceramic.
 13. A method as recited in claim 8, whereinthe metal billet comprises a zirconium based metallic amorphous alloyformed from low purity materials.
 14. A method as recited in claim 13,wherein the zirconium based metallic amorphous alloy comprises at leastone of the compositions selected from the group consisting of(Zr₄₁Ti₁₄Cu_(12.5)Ni₁₀Be_(22.5))₉₈Y₂, (Zr₃₄Ti₁₅Cu_(12.5)Ni₁₁Be₂₈)₉₈Y₂,Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈Y₂, (Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈)₉₈Y₂,(Zr₃₄Ti₁₅Cu₁₀Ni₁₁Be_(22.5))₉₈Y₂, (Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₈Y₂, and(Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₆Y₄.
 15. A method as recited in claim 8, wherein themetal billet comprises at least one of iron, silver, or gold.
 16. Amethod as recited in claim 8, wherein the method is performed undervacuum or in an inert atmosphere.
 17. A method as recited in claim 8,further comprising pressing a surface of the metal within the moldcavity with a pressing member before the metal completely cools.
 18. Amethod as recited in claim 17, wherein the pressing member applies amesh, sawtooth, or textured pattern to a surface of the metal within themold cavity.
 19. A method as recited in claim 8, wherein RF inductionheating of the metal billet melts the metal billet within about 5seconds or less.
 20. A method as recited in claim 8, wherein RFinduction heating of the metal billet melts the metal billet withinabout 1 second or less.
 21. An apparatus for melting and molding anarticle from a solid metal billet, comprising: a mold including a cavityhaving a shape of an article to be molded, at least that portion of themold defining the cavity being formed of ceramic so as to besubstantially not sensitive to heating by RF induction; a delivery chuteincluding a channel for delivering a metal billet from a proximal end toa distal end of the chute, the distal end being adjacent to the cavityof the mold, at least the distal end of the delivery chute being formedof ceramic so as to be substantially not sensitive to heating by RFinduction; an RF induction heating coil surrounding the cavity of themold and the distal end of the ceramic delivery chute; and a pressingmember for selectively pressing a molten metal billet into the cavity.22. A method of manufacturing an orthodontic bracket from metal,comprising: selectively heating a metal billet by RF induction heatingadjacent to a molding cavity defined by a mold, the cavity being in theshape of at least a portion of an orthodontic bracket so as to melt themetal billet such that substantially all of the metal enters the moldingcavity and substantially fills the molding cavity, the mold being formedof a material that is substantially insensitive to heating by RFinduction such that there is substantially no heating of the mold by RFinduction; allowing the metal within the molding cavity to cool so as toform a solid metal orthodontic bracket; and removing the solid metalorthodontic bracket from the molding cavity.
 23. A method as recited inclaim 22, wherein at least that portion of the mold defining the moldingcavity is formed of ceramic.
 24. A method as recited in claim 22,wherein the metal billet comprises a zirconium based metallic amorphousalloy.
 25. A method as recited in claim 24, wherein the zirconium basedamorphous metallic alloy is selected from the group consisting of(Zr₄₁Ti₁₄Cu_(12.5)Ni₁₀Be_(22.5))₉₈Y₂, (Zr₃₄Ti₁₅Cu_(12.5)Ni₁₁Be₂₈)₉₈Y₂,Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈Y₂, (Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈)₉₈Y₂,(Zr₃₄Ti₁₅Cu₁₀Ni₁₁Be_(22.5))₉₈Y₂, (Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₈Y₂, and(Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₆Y₄.
 26. A method as recited in claim 22, wherein themethod is performed under vacuum and/or in an inert atmosphere.
 27. Amethod as recited in claim 22, wherein the molding cavity is configuredsuch that the molten metal enters the molding cavity through an entranceportion of the molding cavity corresponding to a bonding pad of theorthodontic bracket.
 28. A method as recited in claim 27, furthercomprising pressing a surface of the metal within the molding cavityadjacent to the entrance with a pressing member before the metalcompletely cools.
 29. A method as recited in claim 28, wherein thepressing member applies a mesh, sawtooth, or textured pattern to abonding pad surface of the orthodontic bracket.
 30. A method as recitedin claim 29, further comprising bending the bonding pad surface of theorthodontic bracket subsequent to removing the metal orthodontic bracketfrom the molding cavity so as to, form a curved bonding pad withundercuts within the bonding pad surface.
 31. A method as recited inclaim 22, wherein selective heating of the metal billet so as to meltthe metal billet is accomplished substantially simultaneously with themetal entering the molding cavity.
 32. A method of manufacturing anorthodontic bracket from a zirconium based metallic amorphous alloy,comprising: selectively heating a metal billet of a zirconium basedmetallic amorphous alloy material by RF induction heating adjacent to amolding cavity defined by a mold, the cavity being in the shape of anorthodontic bracket so as to melt the metal billet, the metal billethaving a volume substantially equal to a volume of the molding cavitysuch that substantially all of the metal enters the molding cavity andsubstantially fills the molding cavity, the mold being formed of amaterial that is substantially insensitive to heating by RF inductionsuch that there is substantially no heating of the mold by RF induction;allowing the metal within the molding cavity to cool so as to form asolid metal orthodontic bracket; and removing the solid metalorthodontic bracket from the molding cavity; wherein heating and moldingof the orthodontic bracket is performed under vacuum.
 33. A method asrecited in claim 32, wherein the zirconium based metallic amorphousalloy comprises at least one alloy selected from the group consisting of(Zr₄₁Ti₁₄Cu_(12.5)Ni₁₀Be_(22.5))₉₈Y₂, (Zr₃₄Ti₁₅Cu_(12.5)Ni₁₁Be₂₈)₉₈Y₂,Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈Y₂, (Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈)₉₈Y₂,(Zr₃₄Ti₁₅Cu₁₀Ni₁₁Be_(22.5))₉₈Y₂, (Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₈Y₂, and(Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₆Y₄.
 34. A method as recited in claim 32, wherein atleast the portion of the mold defining the molding cavity is formed ofceramic.
 35. A method as recited in claim 32, wherein selective heatingof the metal billet so as to melt the metal billet is accomplishedsubstantially simultaneously with the metal entering the molding cavity.36. A method of manufacturing an orthodontic bracket from metal,comprising: selectively heating a metal billet by RF induction heatingadjacent to a molding cavity defined by a mold formed of a material thatis substantially insensitive to heating by RF induction, the moldingcavity being in the shape of an orthodontic bracket, the metal billetmelting such that substantially all of the metal enters the moldingcavity through an entrance portion of the molding cavity correspondingto a bonding pad of the orthodontic bracket, the metal substantiallyfilling the molding cavity; pressing a surface of the metal within themolding cavity adjacent to the entrance with a pressing member beforethe metal completely cools so as to apply a mesh, sawtooth, or texturedpattern to a bonding pad surface of the orthodontic bracket; allowingthe metal within the molding cavity to cool; removing the metalorthodontic bracket from the molding cavity; and bending the bonding padsurface of the orthodontic bracket so as to form a curved bonding padhaving undercuts within the bonding pad surface.
 37. A method as recitedin claim 36, wherein at least that portion of the mold defining themolding cavity is formed of ceramic.
 38. A method as recited in claim36, wherein the metal billet comprises a zirconium based metallicamorphous alloy.
 39. A method as recited in claim 38, wherein thezirconium based metallic amorphous alloy comprises at least one alloyselected from the group consisting of(Zr₄₁Ti₁₄Cu_(12.5)Ni₁₀Be_(22.5))₉₈Y₂, (Zr₃₄Ti₁₅Cu_(12.5)Ni₁₁Be₂₈)₉₈Y₂,Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈Y₂, (Zr₃₄Ti₁₅Cu₁₂Ni₁₁Be₂₈)₉₈Y₂,(Zr₃₄Ti₁₅Cu₁₀Ni₁₁Be_(22.5))₉₈Y₂, (Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₈Y₂, and(Zr₅₅Al₁₅Ni₁₀Cu₂₀)₉₆Y₄.
 40. A method as recited in claim 36, whereinselective heating of the metal billet so as to melt the metal billet isaccomplished substantially simultaneously with the metal entering themolding cavity.